This invention relates, in general, to semiconductor wafer processing equipment, and more particularly to an apparatus for polishing a semiconductor wafer made of silicon or other material that is used in the fabrication of a semiconductor device.
Semiconductor devices are manufactured on a substrate which is usually made from silicon or the like. The substrate or wafers, are sliced from ingots of various sizes. This slicing process causes surface damage and leaves the wafer with thickness variations and deviations from parallelism. To improve the wafer flatness and parallelism and eliminate saw marks and surface damage, the wafers are sent through a lapping or grinding, and an etching and polishing process.
The rough surface of a lapped wafer is usually etched to remove subsurface damage, then polished to a flat mirror finish before the wafer is suitable for processing into semiconductor devices. The polished wafer must be free from defects and be extremely flat, especially when the wafer is used for sub-micron devices.
Polishing wafers is usually a two part process in which the first part, or primary polish is stock removal, approximately 17 micrometers of material are removed from each wafer. The next step is final polishing, where only a very small amount of material remains to be removed. Both primary polish and final polish are done on the same type of machine but with different slurries and pads. Since final polishing takes only about twenty percent of the time that primary polishing takes, there may be four or five primary polishing machines for each machine used for final polishing.
It was found that the existing polishing equipment was not capable of producing the high quality flat finish that is necessary in the starting material of a sophisticated integrated circuit. It was also found that over two percent of the wafers were damaged due to the manual handling of the wafers during the unloading of the primary polisher, transporting the wafers, and loading the final polisher.
A need therefore existed for an automatic polishing system that could do both the primary and the final polish and still produce large diameter, ultra flat, defect free wafers, with a minimum amount of operator handling.